One example of a high-speed radio transmission technique is the ultra wide band (UWB) communication scheme. The UWB communication scheme is a technique for performing communication in a ultra wide band using a pulse signal sequence formed with pulse signals that synchronize with a predetermined periodic timing. As an example of UWB communication, a method for using a pulse signal sequence formed with extremely-fine pulse signals, having a pulse width of, for example, one nanosecond or narrower, without using a carrier wave, is known. When using this kind of a UWB pulse, because the width of a transmission pulse is extremely narrow, it is known that accurate distance measurement is possible even in a multipath propagation environment.
For example, a UWB pulse signal is transmitted from a UWB reader, which is a radio base station apparatus (hereinafter referred to as “base station”) to a UWB tag, which is a radio terminal apparatus (hereinafter referred to as “terminal”), and after the UWB tag receives the UWB pulse signal, the UWB pulse signal is retransmitted from the UWB tag to the UWB reader. Then, by measuring the round-trip time, it is possible to measure the distance between the UWB reader and the UWB tag.
IEEE802.15.4a (low-rate UWB standard), which is a standard for specifying the physical layer of the UWB low transmission rate, discloses the two-way ranging (TWR) technique (see Non-Patent Literature 1). Non-Patent Literature 1 discloses concrete examples of the accuracy of distance measurement by the difference of frequencies of crystal oscillators between a base station and a terminal, and the improvement method thereof.
Further, Patent Literature 1 discloses a technique for measuring the difference between the transmission-side clock and the reception-side clock by receiving a preamble transmitted from a base station at a terminal, then re-radiating that preamble using the terminal's clock, and measuring the duration at the base station.